For years, farmers have used various styles of rippers to fracture soil and improve crop yields. Recently, in-line rippers that can fracture soil without significantly disturbing the soil surface have gained popularity with farmers. In-line rippers have allowed operators to decrease subsequent tillage passes and improve residue retention of their fields to comply to strict erosion guidelines. Agricultural implements such as deep tillage rippers often are towed by a large four-wheel drive (4WD) tractor, especially if the implement is a larger unit with nine or more standards. A problem can arise when the operator desires to pull an integral ripper, which is normally mounted on a three point tractor hitch, since many 4WD tractors in the size range necessary are not equipped with such a hitch. In addition, some operators prefer frames equipped with drawn rather than 3-point hitches on smaller machines with fewer standards for facilitating tractor changes and for speeding hitching and unhitching operations. It is often desirable to have conversion structure for facilitating pull-type ripper operation with an integral ripper design. Numerous hitch attachments are available for converting an integral ripper to a pull-type ripper. Such attachments typically include a hitch assembly that pins into the existing lower hitch plates of the ripper. A turnbuckle is placed from the upper link attachment location on the ripper to an upper surface of the hitch to facilitate horizontal adjustment of the machine front-to-rear for compensating for different tractor drawbar heights. Independent wheel packages are generally placed off the front of the ripper, one on each side, with a forward acting wheel arm and dual tandem wheels.
Hitch attachments for conversion from integral to pull-type can produce some undesirable conditions. A light hitch condition often results from placement of the majority of the implement weight behind the wheels, a condition that produces high vertical hitch loads on the tractor drawbar in the upward direction. The high vertical loads, in turn, produce high axial loads which pass through the turnbuckle. Other negative attributes of the forwardly located wheels include unstable transport conditions and high stresses on certain areas of the implement frame. A further problem with some wheel arrangements is instability or oscillation of the implement while operating in the field as the front of the frame tends to nose downwardly and then rock back upwardly under certain field conditions.
To eliminate some of the problems, placement of the transport wheels near the rear of the machine is helpful. However, numerous obstacles on the rear of the implement frame limit such wheel placement. Placement of the wheels at the rear of the implement creates undesirable moments tending to rotate the front of the frame downwardly. Maintaining proper machine attitude and uniform working depth is a problem.
Using wheels at both the front and the rear of the implement present numerous problems, including the provision of an economically feasible wheel lift and timing system. Hydraulic controls for all the wheels can be expensive and very complex. Manually adjustable gauge wheels often are difficult to fine tune, particularly when the implement is relatively large and heavy. Providing conversion hitch attachments therefore has presented numerous challenges to the implement designer.
A problem with independent wheel modules, regardless of wheel location, is need for structure to keep the wheels timed. A mechanical timing tube is often impractical because of interference with machine components.
Another conversion structure which is the subject of commonly assigned U.S. patent application Ser. No. 10/298,619, filed 15 Nov. 2002 and entitled STRUCTURE FOR CONVERTING AN INTEGRAL IMPLEMENT TO A DRAWN TYPE. The structure described includes a wheel module with both a forward gauge wheel and a rearward transport wheel. The transport wheels are located behind the center of gravity of the implement for stability, and the forwardly located gauge wheels offset the moment resulting from standard draft. Although alleviating some problems, the module design is complex and relatively expensive to manufacture. Residue flow between the ripper standards and transport wheels is hampered, and blockages can occur in some field conditions. Tire tracking in soft ground is another problem since the transport and stabilizer wheels are located between ripper standards, and the tracks are not fully removed by the standards. The module arrangement also requires depth control wheels and stabilizer wheels to be adjusted to change operating depth. Therefore, depth and pitch control changes can be difficult and time-consuming.